1. Field of the Invention
The present invention relates to RF microelectromechanical systems (RF-MEMS) switches assembled in RF circuit modules for surveillance radar scanners or other devices.
2. Description of the Related Art
As an example of switching devices for RF signals, such as millimeter-wave and microwave signals, a shunt RF-MEMS switch (shunt switching device) is disclosed, for example, in Non-patent Document 1, entitled “High-Isolation CPW MEMS Shunt Switches-Part1: Modeling,” (IEEE Transactions on Microwave Theory Techniques, Vol. 48. No. 6, June 2000, pp. 1045–1052) written by J. B. Muldavin, Student Member, IEEE et al.
This type of RF-MEMS switch includes an RF signal-conducting unit provided on a substrate thereof. Also, an electrode facing at least a portion of the RF signal-conducting unit is disposed above the substrate. In such an RF-MEMS switch, displacing the electrode towards or away from the substrate using electrostatic attraction changes the capacitance between the electrode and the RF signal-conducting unit.
For example, reducing the space between a signal line arranged on the RF signal-conducting unit and the movable electrode increases the capacitance between the signal line and the movable electrode, thus switching off conduction of an RF signal of the signal line. In contrast, increasing the space between the signal line and the movable electrode decreases the capacitance between the signal line and the movable electrode, thus switching on the conduction of the RF signal of the signal line. In other words, in this RF-MEMS switch, varying the capacitance between the movable electrode and the signal line by displacing the movable electrode switches RF signal conduction of the RF signal-conducting unit on or off.
However, since known RF-MEMS switches include one switching device which is provided with only one movable electrode, there is a possibility that insertion loss and return loss of the switch cannot be sufficiently reduced and isolation characteristics of the switch cannot be sufficiently improved.